The present invention relates to telephone switching networks and more particularly to fault locating systems employed therein.
In telephone switching networks, analog electronic switching machines employ switch fabrics which are multiple-input/multiple- output matrices that permit the routing of messages from any calling subscriber to any receiving subscriber. The switch fabrics provide a connection for any of various types of calls including line-trunk, line-line, and trunk-trunk call types from the call originator on the line side of an analog switch to a destination line side of another or the same analog switch.
The switch fabric in each analog switching machine is physically constructed of arrays of grids with each grid containing an electrical switch crosspoint at each intersection of input and output levels. Stored-program network controllers are employed with the analog switching machines to set up a requested connection by closing appropriate crosspoint switches, in all of the corresponding grids, in all of the involved switching machines, to provide the end-to-end path from originator to terminator.
The crosspoint switch actions are implemented by relays that can fail. Additionally, the network controllers that order the proper relays to close and open and the pulse devices that implement the network orders can fail as well. Links between switch grids can also fail. To provide acceptable network availability, it is necessary that connection failures not only be detected but that the root causes of the failures be identified and serviced.
Analog electronic switching machines are normally operated to transmit an error message every time the machine attempts to set up a connection, but the desired connection fails a post-setup continuity test executed by the machine.
In the prior art, failed path messages from an analog switch machine have been listed for interpretation by an operator. The operator, on the basis of system and machine knowledge, manually processed and analyzed the raw error messages in an attempt to determine the root-cause of trouble and thereby to identify fault locations. Typically, collected error message data has been formatted as switch pictures for analysis analyzed from time to time by an operator in an effort to identify failed crosspoints or other connection failures. While crosspoint and other failures have often been located and serviced with use of this maintenance procedure, the methodology has been labor intensive and network availability has not been as high as desirable. Further, customer service has been adversely affected by the time required to isolate and repair connection faults.
Moreover, it has been difficult with known prior art procedures to identify the root causes of connection failures, and certain kinds of connection failures have often appeared to be other kinds of connection failures with the result that unnecessary service costs have been incurred by the replacement of parts in good working order.
Actual failures have been masked by other failures in a number of different ways including the following:
1. a failed pulse device may appear to be a failed crosspoint; PA1 2. a grid link failure may appear to be multiple crosspoint failures; PA1 3. a network controller failure may appear to be failed crosspoints and/or failed pulse devices. PA1 4. stored program execution errors may appear to be any of the above.